High Efficiency Ejector Cycle

ABSTRACT

A system has a compressor ( 22 ), a heat rejection heat exchanger ( 30 ), first and second ejectors ( 38, 202 ), first and second heat absorption heat exchangers ( 64, 220 ), and first and second separators ( 118, 210 ). The heat rejection heat exchanger is coupled to the compressor to receive refrigerant compressed by the compressor. The first ejector has a primary inlet coupled to the heat rejection exchanger to receive refrigerant, a secondary inlet, and an outlet. The first separator has an inlet coupled to the out let of the first ejector to receive refrigerant from the first ejector. The first separator has a gas outlet coupled to the compressor to return refrigerant to the compressor. The first separator has a liquid outlet coupled to the secondary inlet of the ejector to deliver refrigerant to the first ejector. The first heat absorption heat exchanger is coupled to the liquid outlet of the first separator to receive refrigerant and to the secondary inlet of the first ejector to deliver refrigerant to the first ejector. The second ejector has a primary inlet coupled to the liquid outlet of the first separator to receive refrigerant, a secondary inlet, and an outlet. The second separator has an inlet coupled to an outlet of the second ejector to receive refrigerant from the second ejector, a gas outlet coupled to the compressor to return refrigerant to the compressor, and a liquid outlet. The second heat absorption heat exchanger is coupled to the liquid outlet of the second separator to receive refrigerant and to the secondary inlet of the second ejector to deliver refrigerant to the second ejector.

CROSS-REFERENCE TO RELATED APPLICATION

Benefit is claimed of U.S. Patent Application Ser. No. 61/367,100, filedJul. 23, 2010, and entitled “High Efficiency Ejector Cycle”, thedisclosure of which is incorporated by reference herein in its entiretyas if set forth at length.

BACKGROUND

The present disclosure relates to refrigeration. More particularly, itrelates to ejector refrigeration systems.

Earlier proposals for ejector refrigeration systems are found in U.S.Pat. No. 1,836,318 and U.S. Pat. No. 3,277,660. FIG. 1 shows one basicexample of an ejector refrigeration system 20. The system includes acompressor 22 having an inlet (suction port) 24 and an outlet (dischargeport) 26. The compressor and other system components are positionedalong a refrigerant circuit or flowpath 27 and connected via variousconduits (lines). A discharge line 28 extends from the outlet 26 to theinlet 32 of a heat exchanger (a heat rejection heat exchanger in anormal mode of system operation (e.g., a condenser or gas cooler)) 30. Aline 36 extends from the outlet 34 of the heat rejection heat exchanger30 to a primary inlet (liquid or supercritical or two-phase inlet) 40 ofan ejector 38. The ejector 38 also has a secondary inlet (saturated orsuperheated vapor or two-phase inlet) 42 and an outlet 44. A line 46extends from the ejector outlet 44 to an inlet 50 of a separator 48. Theseparator has a liquid outlet 52 and a gas outlet 54. A suction line 56extends from the gas outlet 54 to the compressor suction port 24. Thelines 28, 36, 46, 56, and components therebetween define a primary loop60 of the refrigerant circuit 27. A secondary loop 62 of the refrigerantcircuit 27 includes a heat exchanger 64 (in a normal operational modebeing a heat absorption heat exchanger (e.g., evaporator)). Theevaporator 64 includes an inlet 66 and an outlet 68 along the secondaryloop 62 and expansion device 70 is positioned in a line 72 which extendsbetween the separator liquid outlet 52 and the evaporator inlet 66. Anejector secondary inlet line 74 extends from the evaporator outlet 68 tothe ejector secondary inlet 42.

In the normal mode of operation, gaseous refrigerant is drawn by thecompressor 22 through the suction line 56 and inlet 24 and compressedand discharged from the discharge port 26 into the discharge line 28. Inthe heat rejection heat exchanger, the refrigerant loses/rejects heat toa heat transfer fluid (e.g., fan-forced air or water or other fluid).Cooled refrigerant exits the heat rejection heat exchanger via theoutlet 34 and enters the ejector primary inlet 40 via the line 36.

The exemplary ejector 38 (FIG. 2) is formed as the combination of amotive (primary) nozzle 100 nested within an outer member 102. Theprimary inlet 40 is the inlet to the motive nozzle 100. The outlet 44 isthe outlet of the outer member 102. The primary refrigerant flow 103enters the inlet 40 and then passes into a convergent section 104 of themotive nozzle 100. It then passes through a throat section 106 and anexpansion (divergent) section 108 through an outlet 110 of the motivenozzle 100. The motive nozzle 100 accelerates the flow 103 and decreasesthe pressure of the flow. The secondary inlet 42 forms an inlet of theouter member 102. The pressure reduction caused to the primary flow bythe motive nozzle helps draw the secondary flow 112 into the outermember. The outer member includes a mixer having a convergent section114 and an elongate throat or mixing section 116. The outer member alsohas a divergent section or diffuser 118 downstream of the elongatethroat or mixing section 116. The motive nozzle outlet 110 is positionedwithin the convergent section 114. As the flow 103 exits the outlet 110,it begins to mix with the flow 112 with further mixing occurring throughthe mixing section 116 which provides a mixing zone. In operation, theprimary flow 103 may typically be supercritical upon entering theejector and subcritical upon exiting the motive nozzle. The secondaryflow 112 is gaseous (or a mixture of gas with a smaller amount ofliquid) upon entering the secondary inlet port 42. The resultingcombined flow 120 is a liquid/vapor mixture and decelerates and recoverspressure in the diffuser 118 while remaining a mixture. Upon enteringthe separator, the flow 120 is separated back into the flows 103 and112. The flow 103 passes as a gas through the compressor suction line asdiscussed above. The flow 112 passes as a liquid to the expansion valve70. The flow 112 may be expanded by the valve 70 (e.g., to a low quality(two-phase with small amount of vapor)) and passed to the evaporator 64.Within the evaporator 64, the refrigerant absorbs heat from a heattransfer fluid (e.g., from a fan-forced air flow or water or otherliquid) and is discharged from the outlet 68 to the line 74 as theaforementioned gas.

Use of an ejector serves to recover pressure/work. Work recovered fromthe expansion process is used to compress the gaseous refrigerant priorto entering the compressor. Accordingly, the pressure ratio of thecompressor (and thus the power consumption) may be reduced for a givendesired evaporator pressure. The quality of refrigerant entering theevaporator may also be reduced. Thus, the refrigeration effect per unitmass flow may be increased (relative to the non-ejector system). Thedistribution of fluid entering the evaporator is improved (therebyimproving evaporator performance). Because the evaporator does notdirectly feed the compressor, the evaporator is not required to producesuperheated refrigerant outflow. The use of an ejector cycle may thusallow reduction or elimination of the superheated zone of theevaporator. This may allow the evaporator to operate in a two-phasestate which provides a higher heat transfer performance (e.g.,facilitating reduction in the evaporator size for a given capability).

The exemplary ejector may be a fixed geometry ejector or may be acontrollable ejector. FIG. 2 shows controllability provided by a needlevalve 130 having a needle 132 and an actuator 134. The actuator 134shifts a tip portion 136 of the needle into and out of the throatsection 106 of the motive nozzle 100 to modulate flow through the motivenozzle and, in turn, the ejector overall. Exemplary actuators 134 areelectric (e.g., solenoid or the like). The actuator 134 may be coupledto and controlled by a controller 140 which may receive user inputs froman input device 142 (e.g., switches, keyboard, or the like) and sensors(not shown). The controller 140 may be coupled to the actuator and othercontrollable system components (e.g., valves, the compressor motor, andthe like) via control lines 144 (e.g., hardwired or wirelesscommunication paths). The controller may include one or more:processors; memory (e.g., for storing program information for executionby the processor to perform the operational methods and for storing dataused or generated by the program(s)); and hardware interface devices(e.g., ports) for interfacing with input/output devices and controllablesystem components.

Various modifications of such ejector systems have been proposed. Oneexample in U.S. 20070028630 involves placing a second evaporator alongthe line 46. U.S. 20040123624 discloses a system having twoejector/evaporator pairs. Another two-evaporator, single-ejector systemis shown in U.S. 20080196446. Another method proposed for controllingthe ejector is by using hot-gas bypass. In this method a small amount ofvapor is bypassed around the gas cooler and injected just upstream ofthe motive nozzle, or inside the convergent part of the motive nozzle.The bubbles thus introduced into the motive flow decrease the effectivethroat area and reduce the primary flow. To reduce the flow further morebypass flow is introduced

SUMMARY

One aspect of the disclosure involves a system having a compressor, aheat rejection heat exchanger, first and second ejectors, first andsecond heat absorption heat exchangers, and first and second separators.The heat rejection heat exchanger is coupled to the compressor toreceive refrigerant compressed by the compressor. The first ejector hasa primary inlet coupled to the heat rejection exchanger to receiverefrigerant, a secondary inlet, and an outlet. The first separator hasan inlet coupled to the outlet of the first ejector to receiverefrigerant from the first ejector. The first separator has a gas outletcoupled to the compressor to return refrigerant to the compressor. Thefirst separator has a liquid outlet coupled to the secondary inlet ofthe ejector to deliver refrigerant to the first ejector. The first heatabsorption heat exchanger is coupled to the liquid outlet of the firstseparator to receive refrigerant and to the secondary inlet of the firstejector to deliver refrigerant to the first ejector. The second ejectorhas a primary inlet coupled to the liquid outlet of the first separatorto receive refrigerant, a secondary inlet, and an outlet. The secondseparator has an inlet coupled to an outlet of the second ejector toreceive refrigerant from the second ejector, a gas outlet coupled to thecompressor to return refrigerant to the compressor, and a liquid outlet.The second heat absorption heat exchanger is coupled to the liquidoutlet of the second separator to receive refrigerant and to thesecondary inlet of the second ejector to deliver refrigerant to thesecond ejector.

In various implementations, one or both separators may be gravityseparators. The system may have no other separator (i.e., the twoseparators are the only separators). The system may have no otherejector. The second heat absorption heat exchanger may be positionedbetween the outlet of the second ejector and the compressor. Therefrigerant may comprise at least 50% carbon dioxide, by weight. Thesystem may further include a mechanical subcooler positioned between:the heat rejection heat exchanger; and the inlet of the first ejectorand the inlet of the second ejector. The system may further include asuction line heat exchanger having a heat rejection heat exchanger and aheat rejection leg and a heat absorption leg. The heat rejection leg maybe positioned between: the heat rejection heat exchanger; and the inletof the first ejector and the inlet of the second ejector. The heatabsorption leg may be positioned between the second heat absorption heatexchanger and the compressor suction. The first and second heatabsorption heat exchangers may respectively be in first and secondrefrigerated spaces.

Other aspects of the disclosure involve methods for operating thesystem.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a prior art ejector refrigeration system.

FIG. 2 is an axial sectional view of an ejector.

FIG. 3 is a schematic view of a first refrigeration system.

FIG. 4 is a pressure-enthalpy (Mollier) diagram of the system of FIG. 3.

FIG. 5 is a schematic representation of a first evaporator positioningfor the system of FIG. 3.

FIG. 6 is a schematic representation of a second evaporator positioningfor the system of FIG. 3.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 3 shows an ejector cycle vapor compression (refrigeration) system200. The system 200 may be made as a modification of the system 20 or ofanother system or as an original manufacture/configuration. In theexemplary embodiment, like components which may be preserved from thesystem 20 are shown with like reference numerals. Operation may besimilar to that of the system 20 except as discussed below with thecontroller controlling operation responsive to inputs from varioustemperature sensors and pressure sensors.

The ejector 38 is a first ejector and the system further includes asecond ejector 202 having a primary inlet 204, a secondary inlet 206,and an outlet 208 and which may be configured similarly to the firstejector 38.

Similarly, the separator 48 is a first separator. The system furtherincludes a second separator 210 having an inlet 212, a liquid outlet214, and a gas outlet 216. In the exemplary system, the gas outlet 216is connected via a line 218 to the suction port 24.

Similarly, the evaporator 64 is a first evaporator. The system furtherincludes a second evaporator 220 having an inlet 222 and an outlet 224.The second evaporator inlet 222 receives refrigerant from the secondseparator outlet 214 via a second expansion valve 226 in a line 228. Therefrigerant flow from the outlet 224 of the second evaporator passes tothe second ejector secondary inlet 206 via a line 230.

The second ejector primary inlet 204 receives liquid refrigerant fromthe first separator. This may be delivered by a branch conduit 240branching off the line/flowpath from the first separator to the liquidoutlet 52 to the first evaporator inlet 66 upstream of the valve 70.

In the exemplary embodiment, the compressor is an economized compressorhaving an intermediate port (e.g., economizer port) 244 at anintermediate stage in compression between the suction port 24 anddischarge port 26. The first separator gas outlet 54 is connected to theintermediate port 244 by a line 246.

FIG. 4 shows the two compression stages as 280 (from the suction port 24to the economizer port 224) and 282 (from the economizer port 224 to thedischarge port 26). The compressor discharge pressure is shown as P1whereas the suction pressure is shown as P5. The exemplary suctioncondition is to the vapor side of the saturated vapor line 290. Thefirst evaporator 64 is shown operating in a pressure P3 between thepressures P2 and P5. The second evaporator 220 operates at a pressure P4below P5. P2 and P5 represent the respective outlet pressures of thefirst separator 48 and second separator 210. The exemplary expansiondevices 70 and 226 have inlet conditions at P2 and P5, respectively, ator near the saturated liquid line 292 (e.g., slightly within the vapordome).

In operation, the first ejector may be used primarily to control thehigh side pressure P1 and secondarily the capacity of the firstevaporator. The second ejector may be used to control the capacity ofthe second evaporator. For example, to increase the capacity of thefirst evaporator, the first ejector is opened (e.g., its needleextracted to lower P1); to decrease capacity, it is closed (e.g., itsneedle is inserted to increase P1). To increase the capacity of thesecond evaporator, the second ejector is similarly opened (to decrease,closed). P1 may be controlled to optimize system efficiency. For atranscritical cycle such as using carbon dioxide, raising P1 decreasesthe enthalpy out of the gas cooler 30 and increases the coolingavailable for a given compressor mass flow rate. However, P1 alsoincreases compressor power. There is an optimum value of P1 thatmaximizes system efficiency at a given operating condition (e.g.,ambient temperature, compressor speed, and evaporation temperatures). Toraise P1 to the target value, the first ejector is closed (to lower P1,opened).

A temperature sensor T and pressure transducer P at the outlet of thegas cooler may (also or alternatively) provide inputs used to controlejector opening. For example, such a temperature sensor measures gascooler exit temperature which is an indication of the ambienttemperature. Typically, the measured temperature will be 1-7 F (0.6-4.0C) higher than the ambient temperature. Similarly, the gas cooler exitpressure is strongly correlated to the compressor discharge pressure(e.g., 0.5-5% lower than the compressor discharge pressure). Thus, thetwo sensors provide proxies for ambient temperature and compressordischarge pressure, respectively. For a given measured temperature, ifthe measured pressure is higher than the target value, the controlsystem may cause the first ejector to be further opened (if lower thanthe target value, closed).

Controllable expansion devices 70 and 226 may be used to control thestate of the refrigerant leaving the evaporators 64 and 220. For eachevaporator, a target value of superheat may be maintained. Superheat maybe determined by a pressure transducer and temperature sensor downstreamof the associated evaporator. Alternatively, pressure can be estimatedfrom a temperature sensor at the saturated region of the evaporator. Toincrease superheat, the associated expansion device is closed (todecrease, opened). Too high a superheat value results in a hightemperature difference required between the refrigerant and airtemperature and thus a lower evaporation pressure. If the expansiondevice is to open, then the superheat may go to zero and the state ofthe refrigerant leaving the evaporator will be saturated. This resultsin liquid refrigerant which does not provide cooling and must re-pumpedby the ejector.

Additionally, compressor speed may be varied to control overall systemcapacity. Increasing the compressor speed will increase the flow rate toeach of the two ejectors and therefore to each of the two evaporators.

Although the exemplary system has five controllable parameters(compressor speed, two controllable ejectors, and two controllableexpansion devices), other situations are possible. The compressor may befixed speed, one or both ejectors may be non-controllable, or a TXV orfixed expansion device may be used in place of one or both EXV. Analternative is to use, for example, a passive expansion device such asan orifice which (along with the separator) may be sized to allowevaporator overfeed or underfeed and self correct the evaporator exitcondition. With the fixed speed compressor, capacity may be controlledby simply cycling the system on and off. Also, P1 may be controlled bycontrolling an additional expansion device between the heat rejectionheat exchanger and the first ejector.

FIG. 5 shows an implementation wherein a single airflow 160 passes overboth evaporators 220 and 64. In this example, the airflow passesdirectly between the two evaporators. One possible implementation is toform the two evaporators as separate portions of a single physical unit(e.g., a single array of tubes where the different evaporators areformed as different sections of the array by appropriate coupling oftube ends). The airflow 160 may be driven by a fan 162. One example ofthis is a residential air handling unit 164 for delivering air to aconditioned space 166 (e.g., building/room). In this situation, thesecond evaporator 220 could remove sensible heat while the firstevaporator 64 essentially removes the latent heat. This may be used toprovide humidity control.

FIG. 6 shows a system wherein separate airflows 160-1 and 160-2 aredriven across the evaporators 64 and 220 respectively via fans 162-1 and162-2. Such a system may be used to differently condition differentspaces. For example, a refrigerated transport or fixed-siterefrigeration system, the space 166-1 could be a frozen food storagearea; whereas, the space 166-2 could be a storage area for refrigeratedperishables maintained at a somewhat higher temperature than the space166-1. Alternatively, the two spaces could represent differenttemperature zones of a residential or commercial building.

The system may be fabricated from conventional components usingconventional techniques appropriate for the particular intended uses.

Although an embodiment is described above in detail, such description isnot intended for limiting the scope of the present disclosure. It willbe understood that various modifications may be made without departingfrom the spirit and scope of the disclosure. For example, whenimplemented in the remanufacturing of an existing system or thereengineering of an existing system configuration, details of theexisting configuration may influence or dictate details of anyparticular implementation. Accordingly, other embodiments are within thescope of the following claims.

What is claimed is:
 1. A system (200) comprising: a compressor (22); aheat rejection heat exchanger (30) coupled to the compressor to receiverefrigerant compressed by the compressor; a first ejector (38) having: aprimary inlet (40) coupled to the heat rejection heat exchanger toreceive refrigerant; a secondary inlet (42); and an outlet (44); a firstseparator (48) having: an inlet (58) coupled to the outlet of the firstejector to receive refrigerant from the first ejector; a gas outlet (54)coupled to the compressor to return refrigerant to the compressor; and aliquid outlet (52); a first heat absorption heat exchanger (64) coupledto the liquid outlet of the first separator to receive refrigerant andcoupled to the secondary inlet of the first ejector to deliverrefrigerant to the first ejector; a second ejector (202) having: aprimary inlet (204) coupled to the liquid outlet of the first separatorto receive refrigerant; a secondary inlet (206); and an outlet (208); asecond separator (210) having: an inlet (212) coupled to the outlet ofthe second ejector to receive refrigerant from the second ejector; a gasoutlet (216) coupled to the compressor to return refrigerant to thecompressor; and a liquid outlet (214); and a second heat absorption heatexchanger (220) coupled to the liquid outlet of the second separator toreceive refrigerant and to the secondary inlet of the second ejector todeliver refrigerant.
 2. The system of claim 1 further comprising: afirst expansion device (70) between the first separator liquid outlet(52) and the first heat absorption heat exchanger (64) inlet (66); and asecond expansion device (226) between the second separator (210) liquidoutlet (214) and the second evaporator (220) inlet (222).
 3. The systemof claim 1 wherein: the first and second separators are gravityseparators.
 4. The system of claim 1 wherein: the system has no otherseparator.
 5. The system of claim 1 wherein: the system has no otherejector.
 6. The system of claim 1 wherein: the system has no othercompressor.
 7. The system of claim 1 wherein: the gas outlet (54) of thefirst separator feeds an economizer port of the compressor; and the gasoutlet (216) of the second separator feeds a suction port of thecompressor.
 8. The system of claim 1 wherein: the first heat absorptionheat exchanger is in a first refrigerated space; and the second heatabsorption heat exchanger is in a second refrigerated space.
 9. Thesystem of claim 1 wherein: the refrigerant comprises at least 50% carbondioxide, by weight.
 10. A method for operating the system of claim 1comprising running the compressor in a first mode wherein: therefrigerant is compressed in the compressor; refrigerant received fromthe compressor by the heat rejection heat exchanger rejects heat in theheat rejection heat exchanger to produce initially cooled refrigerant;the initially cooled refrigerant passes through the first ejector; and aliquid discharge of the first separator is split into a first portionpassing to the first ejector secondary inlet (42) and a second portionpassing to the primary inlet (204) of the second ejector.
 11. The methodof claim 10 wherein: the first portion of the liquid discharge of thefirst separator passes to the first ejector secondary inlet through anexpansion device (70) followed by the first heat absorption heatexchanger (64); and the second portion of the liquid discharge of thefirst separator passes to the primary inlet of the second ejector via asecond expansion device (226) followed by the second heat absorptionheat exchanger (220).
 12. The method of claim 10 wherein: a gasdischarge of the first separator passes to an economizer port of thecompressor; and a gas discharge of the second separator passes to asuction port of the compressor.
 13. A system (200) comprising: acompressor (22); a heat rejection heat exchanger (30) coupled to thecompressor to receive refrigerant compressed by the compressor; a firstejector (38) having: a primary inlet (40) coupled to the heat rejectionheat exchanger to receive refrigerant; a secondary inlet (42); and anoutlet (44); a first heat absorption heat exchanger (64) coupled to theoutlet of the first ejector to receive refrigerant; a second ejector(202) having: a primary inlet (204); a secondary inlet (206); and anoutlet (208); a second heat absorption heat exchanger (220) coupled tothe outlet of the second ejector to receive refrigerant; and means forpassing refrigerant from the outlet of the first ejector to the primaryinlet of the second ejector.
 14. The system of claim 13 wherein: themeans is also means for returning refrigerant from the outlet of thefirst ejector to the secondary inlet of the first ejector.
 15. Thesystem of claim 13 wherein: the means comprises a first separator (48)and conduits branching from a liquid outlet (52) of the second separatorto respectively feed the first ejector secondary inlet via the firstheat rejection heat exchanger and directly feed the second ejectorprimary inlet.